Chevrolet Repair: 1986 Chevy Silverado, fly wheel, chevy silverado

Question
My truck keeps grinding the gears off of the starter drive, I have tried shimming the starter and taking them off.  I have tried replacing the starter and even the fly wheel and starter drive.  When I replace any component, the truck will turn over a couple of times and run but it is grinding the teeth off after a couple of starts. What else could be the problem?

Answer
There is a tsb on this , you said you replaced the starter drive on this truck.
the tsb shows a gm starter drive part # 10456422 possibly try the gm part instead
of after market.

Is this the original engine and transmisssion ?

I know this isn't much and i hope it helps.
make sure it is shimmed right also.